The compound engine, in fact, in one of these three forms, may now be
said to be universally adopted in this country; and the question of the
relative value of simple expansion in one cylinder, and of compound
expansion in two or more cylinders, which agitated the minds of some of
our leading engineers ten years ago, is now practically solved in favor
of the latter.


THE MARINE BOILER.

The marine boiler of to-day is in all its main features the same as it
was ten years ago. The single-ended boiler, made with two, three, and
sometimes four furnaces, is the simplest form, and for all powers
under 500 indicated horse power is the most generally adopted. The
double-ended form is largely used. It has been found more economically
efficient than the single-ended form, by as much as ten per cent, in the
writer's own experience. It is generally adopted for engines of large
power, but for small power is inconvenient, owing to its occupying more
room lengthwise in the vessel, and also involving two stokeholds and
therefore more supervision. At one time great difficulty was found
in keeping the bottoms of boilers of this kind tight. Owing to their
length, the unequal expansion due to different temperatures at the
top and bottom caused severe racking strains on the bottom seams and
riveting--so severe in some cases as to rend the plating for a large
part of the bottom circumference of the shell. This difficulty has now
been to a large extent got over, in consequence of the greater attention
given to the form and direction of the water spaces in the boiler
itself, so as to induce circulation of water; the introduction of the
feed-water at the top instead of near the bottom; the more careful
management now usual on the part of engineers; and lastly, the use of